1. Field of Invention
The invention relates to a Coriolis mass flowmeter having a measuring tube that can be excited to oscillation and a magnet assembly serving to generate oscillations and/or to measure oscillations, wherein the magnet assembly comprises at least one permanent magnet and a magnet holder holding the permanent magnet.
2. Description of Related Art
Mass flowmeters that work according to the Coriolis principle have at least one oscillation generator, with which the measuring tube is excited to oscillation. The oscillation of the measuring tube is normally detected with two oscillation sensors. The determination of the mass flowmeter then occurs via the phase shift between the oscillations detected respectively by both oscillation sensors.
The oscillation generator and the oscillation sensor are constructed so that they have a permanent magnet as well as a magnetic coil in order to transfer oscillations electrically onto the measuring tube or to detect oscillations of the measuring tube, which is why it is presently termed magnet assembly. In order to mount the permanent magnet on the oscillation generator or the oscillation sensor, it is, for example, glued into a protective housing surrounding the permanent magnet so that it is protected against damage due to external influences such as impact during transportation or during installation.
German Patent Application DE 10 2008 007 742 A1 discloses a Coriolis mass flowmeter that includes a magnet holder having a protective housing, wherein the magnetic holder is made of plastic. The permanent magnet is placed in the magnet holder and is held by it. The protective housing surrounds the magnet holder and protects the magnet additionally against mechanical damage. The protective units known from the prior art, however, have the disadvantage that due to long-term oscillation stress, the mounting between the plastic magnet holder and the metallic protective housing has to be produced with a comparatively large amount of work.